CN110186949B - Method for rapidly measuring absorption rate of boiling point temperature of material to incident laser - Google Patents

Method for rapidly measuring absorption rate of boiling point temperature of material to incident laser Download PDF

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CN110186949B
CN110186949B CN201910424713.3A CN201910424713A CN110186949B CN 110186949 B CN110186949 B CN 110186949B CN 201910424713 A CN201910424713 A CN 201910424713A CN 110186949 B CN110186949 B CN 110186949B
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wire
boiling point
point temperature
power
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CN110186949A (en
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邹江林
郭士慧
肖荣诗
赵乐
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Beijing University of Technology
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    • G01N25/00—Investigating or analyzing materials by the use of thermal means
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Abstract

A method for rapidly measuring the absorption rate of a material to incident laser at a boiling point temperature belongs to the field of laser material processing. The method is characterized in that: placing a photosensitive material in a transmission light path, respectively recording the shape of an original laser spot and the shape of a laser spot penetrating through a metal wire in the processing process, and knowing the area ratio of the original laser power to obtain the power irradiated on the metal wire; calculating the power required by the welding wire material to be heated to the boiling point according to the wire feeding speed; the ratio of the power required for the material of the welding wire to reach the boiling point to the power acting on the material of the welding wire is the absorption rate of the material to the incident laser light at the boiling point temperature. The invention can simply and rapidly obtain the absorption rate of the material to incident laser under the condition of boiling point temperature.

Description

Method for rapidly measuring absorption rate of boiling point temperature of material to incident laser
Technical Field
The invention relates to a method for measuring the laser absorption rate of a material, belongs to the field of laser material processing, and particularly relates to a method for measuring the incident laser absorption rate of the material at a boiling point temperature.
Background
Compared with other processing heat sources such as electric arcs, electron beams, plasmas and the like, the laser has the advantages of high energy concentration, non-contact processing, small heat influence, good processing flexibility, high processing efficiency, environmental friendliness and the like which are incomparable with other processing heat sources. In recent decades, laser processing technology has been rapidly developed, plays an increasingly important role in a plurality of fields, and relates to military and civil application fields such as aerospace, weapon manufacturing, automobile and ship manufacturing and the like. In laser processing, the biggest characteristic is to utilize the heat effect of laser, so the absorption rate of material to laser in the actual course of working of effective measurement helps analyzing the general law of metal material to laser absorption, has important guiding meaning to further improving laser processing efficiency, material deposit or melting efficiency.
The absorption rate of the metal material to the incident laser light is highly dependent on the material temperature, the material surface state, and the laser action angle, in addition to the influence of the mass fraction of the alloying element of the material itself. In the actual laser processing process, due to the fact that the material is violently melted and evaporated, the laser action surface is at the boiling point temperature, the absorption rate of the material to laser under the boiling point calculated by a conventional method is often lower than the actually absorbed energy, the reason is that the roughness and the incident angle of the surface of the laser irradiation material are randomly changed, and the absorption of the laser energy is greatly improved due to the increase of the roughness and the irradiation condition that the incident angle is near the Brewster angle. Therefore, the absorption rate of the material to laser needs to be simultaneously researched by combining experimental means. In addition, in the process of the penetration type laser processing, the laser energy irradiated on the material is actually unknown, and the technical difficulty of measuring the laser absorption rate of the material is increased.
Aiming at the experimental research of the laser absorptivity of materials, for example, a group of laser absorptivity measuring methods including a beam shaper, a plurality of beam splitters and a power meter disclosed in patent CN 108982392a calculates the absorptivity through the combination of the reflectivity and the thermal radiation of a sample to be measured, but the device is not completely suitable for the high-power laser processing process, and the experimental instrument is easily polluted and damaged by the violent melting and evaporation processes of materials, thereby reducing the measuring precision. Another method is to test the laser absorption rate of the material after coating as described in patent CN106353361A, and combine the analysis and comparison of the finite element temperature field and the experimental temperature measurement result to obtain the laser absorption rate of the coated material. In the simulation calculation, the method still has the problem of applicable precision because many physical parameters depend on the temperature of the material and are not in a linear relation. Although the currently known experimental measurement device achieves higher measurement accuracy, the measurement condition is too complex, and strict limiting conditions are provided for experimental materials, laser energy and the like, so that the application range is limited. In view of the above, there is a need for an effective method for measuring the laser absorption rate of a material at a boiling temperature.
The method comprises the steps of utilizing the characteristic that laser acts on a filamentous material to be measured and irradiates a photosensitive material to present the geometrical shape of laser irradiation spots, measuring the residual spots and the original spots penetrating through the filamentous material in the high-power laser material processing process to obtain an area ratio, and calculating according to the emergent light power to obtain the laser power irradiated on the material acting surface; then, the power required by melting and evaporating the material is obtained according to a heat conduction equation, and the ratio of the power to the melting power and the evaporating power is the absorption rate of the material with the boiling point temperature under the processing condition to the laser.
Disclosure of Invention
The invention provides a method for measuring the laser absorptivity of a metal material under a boiling point, which is suitable for the machining processes of wire-feeding laser additive manufacturing, powder-feeding laser additive manufacturing, laser penetration welding, laser filler wire welding, laser cutting and the like.
A method for rapidly measuring the absorption rate of a material to incident laser at a boiling point temperature is characterized in that: placing a photosensitive material in a transmission light path, and recording the shape of a light spot at the current position; calculating the power required by the welding wire material to be heated to the boiling point temperature according to the wire feeding speed; in the wire feeding process, the violent evaporation of the wire leads part of laser beams to penetrate through the wire without participating in the action, so that S is developed by comparing original light spots on the photosensitive material0And developing the laser spot not participating in the action of the wire material in the light-wire stabilization process1Knowing the original laser power P0The laser power (S) irradiated on the wire material in the stabilizing process can be obtained0-S1)/S0×P0) (ii) a The ratio of the power required by the welding wire to absorb the laser energy to reach the boiling point temperature to the power irradiated on the welding wire is the absorption rate of the material to the incident laser at the boiling point temperature.
Further, the laser is in a focusing state, the energy of the facula is in average distribution or Gaussian distribution, and the power of the laser is 0.2 kW-30 kW; the material to be measured is filamentous, and the diameter of the material to be measured is 0.5 mm-3 mm; the included angle between the light beam and the filament is 10-80 degrees; the wire feeding speed is 0.5m/min to 50 m/min; the included angle between the plane of the photosensitive material (photographic paper, photosensitive screen or other photosensitive material) for measuring the shape of the light spot and the light beam is 10-90 degrees; the welding mode of the laser on the welding wire is a deep melting mode.
S1, placing the photosensitive material in a transmission light path, and recording original light spots, light spots which penetrate through the wire material and do not participate in the action process of the laser and the metal wire at the same position; comparing the sizes of the front and rear light spots acting on the wire on the photosensitive material to obtain the laser power P1 actually irradiated on the metal wire in the processing process;
s2 known wire feed speed VsWire diameter d and wire density at boiling point temperature ρ, specific heat capacity c and latent heat of fusion LmBoiling point temperature TvAccording to the formula
Figure GDA0002105958000000031
And (3) obtaining the ratio of the laser power P2, P2 and P1 required by the metal wire to reach the boiling point under the condition, namely the absorptivity of the metal wire to the laser at the boiling point temperature under the condition.
The method for measuring the laser absorption rate of the material at the boiling point temperature has the main process parameters that the type of the laser is not limited to a fiber laser and CO2Lasers of high power such as lasers; the laser power is set within the range of 0.2kW to 30 kW; the diameter of the metal wire is 0.5mm to 50mm, and the angle between the metal wire and the laser is 10 degrees to 90 degrees.
Compared with other technologies for measuring the absorptivity of materials, the method has the following beneficial effects: the method utilizes the photosensitive material to present a more accurate presenting spot shape, can more accurately measure and calculate the laser energy actually irradiated on the material surface in the processing process according to the area ratio before and after processing, and can quickly obtain the laser absorption rate of the metal material at the boiling point under the processing condition through simple calculation.
Drawings
FIG. 1 is a schematic diagram of developing residual transmission spots in a laser additive manufacturing process for photographic paper;
FIG. 2 is a photograph paper receiving original laser spots and remaining transmission spots for development;
FIG. 3 is a schematic representation of CO implementation2A process diagram of laser cutting a massive metal material;
in the figure, 1, photographic paper, 2, laser beam, 3, metal wire, 4, angle adjustable arc plate, 5, laser working head, 6, melting material, 7, cutting surface, 8, laser cutting head, 9, material moving direction
Detailed Description
The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the following examples.
Example 1
As shown in fig. 1, the device for measuring the boiling point absorption rate of a material comprises a photosensitive material FB photographic paper 1, an optical fiber laser beam 2, a metal wire 3, an angle-adjustable arc plate 4 and a laser working head 5. The FB photographic paper 1 is subjected to overexposure pretreatment, and in order to greatly reduce the energy density of laser spots, spots with diameters of more than 30mm are obtained through defocusing; the plane of the FB photographic paper 1 is perpendicular to the central axis of the laser beam; the angle of the metal wire 3 of the laser working head 5 is adjustable on the angle-adjustable arc plate 4; the wire is fed at a certain speed.
In the embodiment, a YLS-6000 fiber laser is adopted, the wavelength of the laser is 1.07 mu m, and the light output power is 1500W; the metal wire is made of 316L stainless steel material with the diameter of 1.2mm, and the wire feeding speed is 1.2 m/min; the included angle between the metal wire and the central line is 15 degrees, and the included angle between the laser beam and the central line is 30 degrees. First, the original spot shape is ablated, and as shown in FIG. 2(a), the spot area S is calculated0(ii) a During the stable wire feeding process, the residual light spots penetrated by the laser after acting on the metal wire are ablated on the photographic paper again as shown in figure 2(b), and the area S is calculated1(ii) a Calculating the laser power irradiated on the metal wire according to the ratio of the two areas and the light emitting power; according to equation 1:
Figure GDA0002105958000000041
and calculating the ratio of the power required when the material reaches the boiling point temperature under the wire feeding speed condition to the laser power received by the metal wire, namely the absorption rate of the metal wire for actually absorbing the laser energy under the experimental condition.
Example 2
The same parts of this embodiment as embodiment 1 are not described again, except that:
1) as shown in FIG. 3, CO was performed2Laser cutting blockIn the process of forming the metal material, the measured data is the metal material pair CO of the cutting surface 72The absorption rate of the laser light.
2) As shown in fig. 3, the cut material moves to the left at a certain speed 9, and the laser cutting head 8 is stationary relative to the photographic paper 1.
The above description is only two specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (2)

1. A method for rapidly measuring the absorption rate of a material to incident laser at a boiling point temperature is characterized in that: placing a photosensitive material in a transmission light path, and recording the shape of a light spot at the current position; calculating the power required by the welding wire to be heated to the boiling point temperature according to the wire feeding speed; in the wire feeding process, the violent evaporation of the wire leads part of laser beams to penetrate through the wire without participating in the action, so that S is developed by comparing original light spots on the photosensitive material0And developing the laser spot not participating in the action of the wire material in the light-wire stabilization process1Knowing the original laser power P0Obtaining the laser power (S) irradiated on the wire material in the stabilizing process0- S1)/ S0× P0) (ii) a The ratio of the power required by the wire material to absorb the laser energy to reach the boiling point temperature to the power irradiated on the welding wire is the absorption rate of the wire material to the incident laser at the boiling point temperature.
2. The method of claim 1, wherein: the laser is in a focusing state, the energy of light spots is in average distribution or Gaussian distribution, and the laser power is 0.2 kW-30 kW; the diameter of the wire is 0.5 mm-3 mm; the included angle between the light beam and the filament is 10-80 degrees; the wire feeding speed is 0.5 m/min-50 m/min; the included angle between the plane of the photosensitive material for measuring the shape of the light spot and the light beam is 10-90 degrees; the welding mode of the laser on the wire is a deep melting mode.
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JPH06246477A (en) * 1993-03-02 1994-09-06 Hitachi Zosen Corp Improvement of absorptivity of laser beam
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CN104029395A (en) * 2014-05-31 2014-09-10 大连理工大学 Method for quickly determining laser power in laser near-net forming process
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